1. Field of the Invention
This invention relates to an electric vehicle (EV) having an engine in combination with a motor as power sources, that is, a hybrid vehicle.
2. Description of the Related Art
An electric vehicle (EV) is a vehicle whose original source of energy is electric power, and is generally driven by the rotational energy of a vehicle driving motor mounted on the vehicle. As a system structure of the electric vehicle, a combination of a vehicle driving motor and an engine is known, and an electric vehicle having such a structure is called a hybrid vehicle. Hybrid vehicles can be grouped into series hybrid vehicles (hereinafter referred to as SHV) and parallel hybrid vehicles (hereinafter referred to as PHV), depending on the connecting relationship between the engine and the vehicle driving motor.
In the SHV, a generator is driven by the engine, and the generated power (from the generator) is used together with power discharged from the battery for driving the vehicle driving motor. The battery can be charged by generated power from the generator or regenerated power from the vehicle driving motor, as well as by an external power supply. In this type of vehicle, the engine is not mechanically coupled with driving wheels, and accordingly, it can be driven within an excellent range of emission and engine efficiency, occasionally allowing the engine to be stopped during travelling. Thus, the SHV has such advantages that the battery does not need to be often charged by an external power supply, and that the vehicle is low pollutive and highly economical.
On the other hand, in one kind of the PHV, the output shaft of the engine is coupled with the output shaft of the rotational electrodynamic unit for assisting the engine. Accordingly, the output torque from the engine and the output torque from the rotational electrodynamic unit are supplied in parallel to the driving wheels (i.e. both torque values are added together and the sum is supplied to the driving wheels). In this structure, for instance, during acceleration, the rotational electrodynamic unit functions as a motor, while during braking, it functions as a generator. More particularly, the rotational electrodynamic unit is capable of supplementing the increase of the required output to the engine (i.e. motor function) for assisting acceleration, and of storing a surplas of the required output to the engine as electric power (i.e. generator function) during braking assist. Additionally, during the braking operation, the braking energy can be collected as electric power and stored in the battery, which obviates the need to often charge the battery from the external power source and results in low pollution and high economy.
These SHV and PHV have another advantage in that travelling can be continued using motor energy even when the engine is stopped due to, for example, fuel shortage or fuel saving. For instance in the SHV, even when the engine is stopped, only generator output is shut down and the vehicle keeps travelling using power supplied from the battery. Also, in the PHV, with a structure in which a clutch is provided between the engine and the rotational electrodynamic unit as is disclosed in Japanese Laid-Open Patent No. Hei 5-49105, opening the clutch causes the engine to stop working as a load, and therefore, the vehicle itself can be kept being driven by output from the rotational electrodynamic unit even after the engine has stopped.
However, in the SHV and PHV, upon stopping the engine, mechanical appliances mounted on the vehicle are no longer operated. Meanwhile, if using the engine only for the operation of the mechanical appliances, the engine revolution speed is decreased up to around the idle speed and the engine efficiency is reduced to as low as 30% of its peak value.
The appliances mounted in the vehicle include, for example, an alternator for appliance battery charge, a pump for a power steering system (P/S), a compressor for an air conditioner (A/C), and a vacuum pump for braking pedal assist. In principle, these appliances can be driven both mechanically and electrically. Mechanical output of the engine is used for mechanically operating the appliances, while generated power from the generator (in the SHV) or rotational electrodynamic unit (in the PHV) is used for electrically operating the appliances. In view of this, the above mentioned inconvenience can be avoid by employing a structure of electrical operation of the appliances using generated power.
However, depending on the selection between mechanical operation or electrical operation of the appliances, the actual configuration of the appliances must be changed. In reality, engine vehicles (having only an engine to supply driving power) are widely manufactured and generally available, and the mechanical activating structure is preferably selected and mass-produced for the appliances. Accordingly, an electrical activating structure for the appliances is expensive compared to the mechanical activating structure, resulting in increased expense for the entire vehicle. It may be possible to add a converter device for converting the generated output into mechanical power and to employ a mechanically driven structure for the appliances. However, this means that the number of the additional electrical devices is increased, also leading to increased cost. Furthermore, depending on the types and functions of the appliances (e.g. in a vacuum pump for braking pedal assist), the energy efficiency of the appliance system can be more preferably maintained by mechanical output of the engine.